RFR: 8351458: (ch) Move preClose to UnixDispatcher

[Jaikiran Pai]

On Tue, 11 Mar 2025 04:25:24 GMT, Jaikiran Pai <jpai at openjdk.org> wrote:

> There used to be a if (reader != 0 || writer != 0) {...} check before doing any of this pre-close work, in DatagramChannelImpl. Is that no longer needed?

Looking at the implementation of `NativeThread.isNativeThread()` and `NativeThread.isVirtualThread()`, it already implicitly takes into account the `!= 0` check, so I guess the previous explicit checks before calling those methods was redundant.

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PR Review Comment: https://git.openjdk.org/jdk/pull/23956#discussion_r1988381093